The present invention relates to novel gold(I) mercaptocarboxylic acid esters which are characterized by a tricycloalkyl group in the alcohol component of the ester. The present invention also concerns a method of preparing these new gold mercaptides and their use in gold preparations for gilding solid bases.
So-called gold preparations have long been used to apply a gold decoration onto ceramic articles and to produce strip conductors of gold in integrated circuits. Such preparations generally contain one or several sulfur-organic gold compounds soluble in an organic carrier medium, fluxing agents such as e.g. resinates of one or several of the elements B, Si, V, Cr, In, Sn, Sb, Bi, and Rh, and the carrier medium contains a resin and organic solvent. The gold preparations are applied onto the surface to be coated and after the evaporation of the solvent, a burning process follows at a temperature adjusted to the substrate and the gold preparation, during which the gold film is formed and fixed with good adhesion to the surface.
The sulfur-organic gold compounds have long been almost exclusively so-called gold sulforesinates which were obtained from a gold salt and sulfurized terpenes, especially naturally occurring terpenes. One disadvantage of these sulforesinates is that their preparation is associated with naturally occurring raw materials whose supply is limited and whose quality is subject to variations. In order to eliminate these disadvantages, and at the same time influence the properties of the gold preparations in a purposeful manner, purely synthetically prepared gold(I) mercaptides with very different structures have been used in the gold preparations.
German patent 12 86 866 teaches defined, secondary gold(I) mercaptides with the formula RR'CH-S-Au in which R and R' signify alkyl, cycloalkyl, aryl or alkylaryl. The use of these gold(I) mercaptides required the use of strongly polar solvents such as nitrobenzene. Tertiary gold(I) mercaptides with the formula RR'R"C-S-Au with R, R' and R" equal to alkyl are soluble according to DE-AS 12 98 828 in slightly polar solvents (e.g., toluene); in addition, these mercaptides exhibit lower decomposition temperatures. Finally, aromatic gold(I) mercaptides with the formula Ar-S-Au have also been suggested for gilding preparations (German patent 12 84 808). A bicyclic mercaptide, namely gold(I) bornyl mercaptide (U.S. Pat. No. 4,221,826), proved to be advantageous for the production of integrated electronic circuits. The above-named gold(I) mercaptides have the disadvantage of a partially very unpleasant odor which becomes particularly noticeable in a disturbing manner when the gold preparations are applied by heat (e.g., by means of hot screen printing).
DE-AS 12 92 463 teaches argentiferous (i.e., silver containing) gilding preparations containing a coordination compound consisting of a gold(I) mercaptide and an equimolar amount of a silver carboxylate or silver mercaptide. Primary or secondary alkyl- or alkylarylmercaptides and also gold(I) mercaptides of 2-methoxyethyl-, ethyl-, isooctyl- and tert.-dodecylthioglycolate are described as the gold(I) mercaptide. These coordination compounds are distinguished by greater solubility and better coating power in comparison to the individual compounds. The coordination compounds have the disadvantage that silver compounds are obligatorily present in equimolar amount and the creation of the decoration is thus limited in regard to the color. Moreover, the decorations are very susceptible to tarnishing phenomena due to the high silver content.
The family of gold(I) thioglycolic acid esters has a considerably more pleasant odor than the above-mentioned gold(I) mercaptides free of carboxyl groups.
Of the gold(I) thioglycolic acid esters cited in DE AS 12 92 463, only gold(I) isooctylthioglycolate and gold(I) tert.-dodecylthioglycolate are basically suitable (in the absence of a stoichiometric amount of a silver compound) for use in gilding preparations in which a gold compound soluble in organic solvents is required (e.g., in bright gold preparations). Gold(I) ethylthioglycolate and gold(I)-2-methoxyethylthioglycolate are compounds which are almost insoluble in organic solvents.
However, as Applicants determined, the previously named isooctyl- and tert.-dodecyl-gold(I) thioglycolates are not satisfactorily suitable in gilding preparations, especially for the decoration of ceramic materials, because the drying time of the preparations is very long. This has a very negative influence on the economy of the decoration.